You may watch this video:
http://zendaya-coleman.com/wordpress/?p=775
The girl here is probably the most famous of the Zendayas out there and maybe the reason for the popularity of the name.
It's hard to say for sure whether this
Shona language angle is right, but anyway it seems that her father is from Zimbabwe where the people speak that language.
Rene www.BabyNames.ch